There are two notable examples of prior art relative to this invention. Both of these use binary polarization switching between two orthogonal polarization states rather than the continuous polarization phase retardation disclosed here.
One example of prior art is a previous invention by Perlin (U.S. Pat. No. 6,061,084, incorporated by reference herein) which uses a variable pitch parallax barrier comprised of a Pi cell (a Pi cell is a binary polarization switching device that can be switched at approximately 200 cycles per second) used to produce alternating opaque and transparent vertical stripes on a light-blocking screen which is placed 50–100 mm in front of an image-producing screen. At any moment in time, each of the viewer's two eyes sees a different image through the transparent gaps between the opaque Pi cell stripes. The pattern of Pi cell and image stripes are determined by the viewer's head position. Specifically, the pitch between the stripes is inversely related to the distance of the viewer to the display.
In the preferred embodiment of that invention, the clear gaps (and the image stripes behind them) are ⅓ the width of the opaque stripes. The gaps and corresponding image stripes simultaneously shift between 3 different positions or phases in a repeating cycle, so that at the end of each cycle every pixel has been seen by each eye, but different columns of pixels have been seen at different times. Thus each pixel alternates between right eye information, left eye information and black (no information). Using three phases in the cycle permits the use of a black buffer stripe of ½ the image stripe width on the side of each image stripe, thereby allowing for slight misregistration of stripe positions relative to actual head position. Without the buffer stripes, any misregistration errors would appear very visibly as vertical slits of crosstalk between the two different images.
Another example of prior art by Kleinberger et al. (U.S. Pat. Nos. 6,252,707, 5,973,831, 5,822,117, incorporated by reference herein) typically uses two binary polarization switching devices, one adjacent to the screen and another spaced further away from the screen in a manner similar to that described above. The polarizing device next the screen is used to polarize the display in alternating orthogonal polarizations (i.e. left and right handed, vertical and horizontal, or −45 and +45 from vertical, respectively). The second polarizing device also presents a set of alternating polarization stripes, such that each eye see different parts of the screen through different sets of stripes matching up in polarization along the lines determined by the rays between the screen and each eye. In another variation of this invention, the second barrier stripes are calculated so that the entire image is only visible from one eye. By activation of a third, uniform polarization switching layer, the entire image becomes visible only to the other eye. In yet another variation of this invention, alternating clear and opaque stripes are used to separate left and right eye view via parallax as in Perlin U.S. Pat. No. 6,061,084, incorporated by reference herein, but with only two phases. It should be noted that as stated above, all of these two phase binary systems in Kleinberger et al. (U.S. Pat. Nos. 6,252,707, 5,973,831, 5,822,117, incorporated by reference herein) lead to visible banding artifacts, due to crosstalk even with minor misregistration of the system relative to actual eye position. To mitigate this, fixed black buffer areas can be utilized around the image stripes, and Kleinberger et al. (U.S. Pat. Nos. 6,252,707, 5,973,831, 5,822,117, incorporated by reference herein) stipulate that optical devices such as lens arrays can be used to fill in the resulting blank areas. Also, Kleinberger et al. (U.S. Pat. Nos. 6,252,707, 5,973,831, 5,822,117, incorporated by reference herein) also propose an implementation using a checkboard pattern instead alternating stripes to spatially interlace the left and right eye views.